In the past, various different methods and devices have been utilized to initiate and control a defrost cycle for a conditioning system, such as for instance that associated with a heat pump or the like. A heat pump is selectively reversibly utilized in a cooling mode to remove heat from a preselected indoor space during the summer and in a heating mode to effect the heating of such space in the winter. For instance, heat pumps are provided with an indoor heat exchanger and an outdoor heat exchanger with a compressor reversibly interconnected therebetween. Thus, when the heat pump is in the cooling mode thereof, the indoor heat exchanger operates as an evaporator, and when the heat pump is in the heating mode thereof, the outdoor heat exchanger operates as an evaporator. Fans may be employed in the heat pump to circulate indoor air over the indoor heat exchanger and outdoor air over the outdoor heat exchanger, respectively, during either the cooling mode operation of the heat exchanger or the heating mode operation thereof.
When the heat pump is being operated in the heating mode thereof, the occurrence of certain conditions, such as atmospheric or outside temperature and high humidity or the like for instance, may cause the accumulation of frost on the outdoor heat exchanger of the heat pump. Of course, such an accumulation of frost on the outdoor heat exchanger inhibits heat transfer between the outdoor heat exchanger and the outdoor air being circulated thereover which serves to reduce the efficiency of the heat pump. Furthermore, it is believed that if a frost layer is permitted to accumulate without interruption on the outdoor heat exchanger, the compressor motor of the heat pump and/or other components thereof might be damaged; therefore, various schemes have been employed in the past to effect defrosting of the outdoor heat exchanger of the heat pump.
For instance, in the heating mode operation of the past heat pumps, various devices were utilized in an attempt to correlate conditions, such as for instance outside atmospheric temperature, outside heat exchanger temperature, and refrigerant temperature in the outside heat exchanger, all of which may be indicative of frost accumulation, in order to measure or otherwise ascertain frost build-up on the outdoor heat exchanger of such past heat pumps. When these sensing devices were operative to indicate a need for effecting defrosting of the accumulated frost in the outdoor heat exchanger, the past heat pumps were reversed so as to effect heating of the outdoor heat exchangers in an attempt to reduce the accumulated frost thereon, and with some of such past heat pumps, an auxiliary heating system was energized to effect heating of the preselected indoor space thereby to counteract the air conditioning or cooling of such preselected space by the heat pump upon the reversal thereof to reduce the frost on the outdoor heat exchanger. Of course, when the outdoor heat exchanger of the past heat pumps was being heated to rid it of accumulated frost, it is believed that any fan circulating outdoor air over the outdoor heat exchanger was deenergized.